1. Field of the Invention
This invention relates to nuclear reactors, and more particularly provides a variable stiffness support system for support structure in the annular region of a condenser type reactor containment.
2. Description of the Prior Art
Commercial nuclear reactors typically include a primary reactor system circulating a fluid coolant through a reactor core. The primary system is enclosed in a reactor containment building. Consistent with the stringent safety oriented attitudes of the nuclear industry, the containment is designed to withstand a pressure transient under assumed major accident conditions. A particular containment design includes a fusible material such as ice, in the solid state, supported in a lattice within an annular region surrounding the primary system to quench the pressure transient. This "condenser" type containment is more fully described in U.S. Pat. No. 3,423,286.
Within the annular region are not only large quantities of the fusible material typically held in baskets supported in a lattice structure, but also cooling ducts extending vertically about sixty feet, to circulate a cooling medium, such as air, thereby maintaining the fusible material in solid form. Support of the lattice and the ducts has, in the past, been performed by massive mechanical structures which include a multitude of fasteners. This large and complex support structure resulted from stringent design limitations including (1) the need for insulating the support structure from the atmospheric temperature surrounding the primary system, (2) the large pressure loading on the outer surface of the cooling ducts under accident conditions, and (3) the large mechanical loadings transmitted to the structure under seismic or other abnormally high mechanical loadings. Also, these limitations, particularly the latter, are variable with each nuclear plant, and therefore required provision of separately designed support structure with different frequency response at each individual plant.
The prior art support structures therefore include a large beam rigidly affixed to the annulus wall, heavily insulated, with numerous connections to the ducts and the lattice, both of which are supported from the beam. The beam transmits both duct and lattice loads to the concrete or steel wall of the annulus. The structure must be specifically designed for proper seismic response, including different beams for each reactor plant.
It is highly advantageous to provide a support structure that minimizes the massive support structures presently designed, that is easily adjustable for plant sites with varying seismic spectrums, that minimizes the amount of fasteners, and that is compatible with existing duct and lattice structures.